Effect of annealing on the structural, topographical and optical properties of sol–gel derived ZnO and AZO thin films

A comparative study of the physical properties of undoped Zinc Oxide (ZnO) and Al doped Zinc Oxide (AZO) thin films were performed as a function of annealing temperature. The structural properties were analyzed using X-ray diffraction and the recorded patterns indicated that the crystallinity of the films always enhanced with increasing annealing temperature while it degrades with Al doping. The topographical modification of the films due to heat treatment was examined by atomic force microscopy which revealed that annealing roughened the surface of all the films; however the AZO films always exhibited smoother morphology than ZnO. Study of the optical properties by UV-Visible spectrophotometer demonstrated that the transmittance was gradually diminished with the rise in annealing temperature. In addition, a notable increase in the optical band gap was also observed for the AZO films.

► C-axis oriented ZnO thin films were grown on quartz substrate using sol–gel.
► No preferred growth orientation was observed for Al doped ZnO.
► Crystallinity and RMS roughness of ZnO and AZO films were enhanced upon annealing.
► Transmittance of all films was decreased with the rise in annealing temperature.
► A notable increase in the optical band gap was observed for the AZO thin films.